6  Geographical data computing

This chapter is about re projecting geographical layers, adding external or personal layers as the flow map background, and their customization.

First you can project or reproject your layers.

6.1 (re)Projecting layers

The cartographic projection of the layers can be changed, by choosing one of the proposed formulas in the projection menu.

Example: several projections applied on the RICardo world trade map

6.2 Geographical layers

The management of the map background is related to the geographic information. It can be accessed via the Layer button, and is composed of three sub-sections.

6.2.1 Add reference layer

Add reference layers consists in calling a remote geographic information layer from Natural Earth data features, to contextualize the flowmap.

Selected reference layers are:

• geographical graticules are grids at 5, 10, 15, 20 and 30° intervals. Includes WGS84 bounding box. See details…

  Example: Add graticule layer 20° interval

  

• world’s countries divisions at spatial resolutions of 110 meters or 50 meters, and the disputed areas. See details…

Example: countries

• world urban areas (of dense human habitations) coverage derived from MODIS satellite, at spatial resolutions of 50 meters or 10 meters. See details…

• world landscape based on lands including major islands. See details…

For all these layers, their fill and stroke can be defined by picking colors, then click on Add layer button.

6.2.2 Add tile layer

The Base type of tiles layers come from Open Street Map (OSM) tile server, CARTO DB and ESRI tile server.

6.2.3 Add Geojson layer

Import Geojson is to load a personal vector layer.

6.3 Types of actions on a layer displayed

Several actions can be performed on all the layer level displayed, via the layer management section using icon-buttons.

Visible/invisible the layer.

Semiology parameters of flow features (nodes and links) : color, size, text, opacity.

Geometry parameters for changing links/arrows shape only. This is not available for nodes). It is possible to change their orientation, the type of link (curve, triange, …) and arrow head parameters.

Definitively deletes the layer.